In this work, the nanocrystalline ZnO/polycrystalline(poly) aluminum nitride(AlN)/ Si-layered structure was fabricated for humidity sensor applications based on surface acoustic wave(SAW). The ZnO film was used as a sensitive material layer. The ZnO and AlN(0002) were deposited by a sol-gel process and a pulse reactive magnetron sputtering, respectively. The ZnO sensitive films coated on AlN have a hexagonal wurtzite structure after the thin films annealed at $400^{circ}C$, $500^{circ}C$ and $600^{circ}C$. The surface of the film exhibits sponginess and a nanometer particle size(below 50 nm). The largest shift in the frequency response was at approximately 200 kHz(the relative humidity: 10 %~90 %) for the structure annealed at $400^{circ}C$. The effect of the change in the environmental temperature on the frequency response of the SAW humidity sensor was also investigated.